Most power wheelchairs utilize two electric drive motors (one on each side) which are coupled to the drive wheels by drives such as pulleys and belts, gears, sprockets and chains, and cog on tire. The powered wheelchairs are differentially steered (similar to a tank). Both drive wheels are driven forward when going forward, whereas the inside wheel is slowed, stopped, or even reversed when turning. Both drive wheels are driven in reverse when going backwards.
FIGS. 1 and 2 show a prior art powered wheelchair 10 having a frame 12, two drive wheels 14 and 16 rotatably connected to the rear of the frame 12, and two non-drive wheels 18 and 20 rotatably connected to the front of the frame 12. The powered wheelchair 10 also includes a power transmission which comprises two motors 22 and 24 and respective drives 26 and 28. The drive 26 couples the motor 22 to the drive wheel 14, and the drive 28 couples the motor 24 to the drive wheel 16. A battery 30 supplies power to the motors 22 and 24.
The powered wheelchair 10 further includes a control system which controls the speed and direction of the motors 22 and 24. Electric brakes 34 and 36 are attached to the shafts of respective motors 22 and 24 to provide braking force thereto.
The motors 22 and 24 drive the powered wheelchair 10 in one speed range. Typically, the maximum wheelchair velocity is in the speed range of less than six miles per hour. The powered wheelchair 10 is therefore limited in speed. Although the lower speed range is beneficial for certain wheelchair functions, such as hill climbing, or powering over obstacles, the low speed range is not always preferable on flat terrain. Wheelchair operators often demand that their wheelchairs perform at higher speeds on flat terrain. Some operators desire speeds in the eight to ten miles per hour range, or higher. These wheelchair operators do not, however, want to sacrifice the low speed ranges (which are necessary for hill climbing) to achieve the higher speeds. The powered wheelchair shown in FIGS. 1 and 2 is incapable of achieving the desired mixture of low speeds for hill climbing and high speeds for flat terrain.
One approach to overcome this problem is to employ a two-speed gearbox with each motor 22 and 24. A two-speed gearbox would enable the wheelchair operate at low speeds when climbing hills or moving over obstacles, and to operate at high speeds when on a flat surface. This approach, however, has limitations in that the transmission system is mechanically complex.
Therefore, the present invention provides a different, and mechanically more simple, approach to solving the above-mentioned problem. The present invention provides a powered wheelchair which employs multiple motors for each drive wheel. Each motor drives the drive wheel in a different speed range, thereby permitting the wheelchair to achieve higher speed ranges without compromising the necessary low speed range for hill climbing and indoor travel.